The present invention relates generally to a process for reducing a greenhouse gas emission component of a combustion gas from a thermal power generation plant.
The applicant has as disclosed in International patent application No. PCT/AU96/00619 developed a method of reducing greenhouse gas emissions in a combustion gas from a power station. The method involves passing the combustion gas from an exhaust stack of the power station through a catalytic converter to enrich the level of NOX in the gas. The enriched combustion gas is then diverted to a gloryhole spillway of the power station where the enriched combustion gas together with its greenhouse gas emissions is contacted with cooling seawater being discharged form the station. The applicant has found that contacting the combustion gas with seawater flowing through the gloryhole spillway is a relatively inefficient way of absorbing or dissolving the greenhouse gas emissions which are then released to the ocean.
An object of the present invention is to provide a process for efficiently reducing greenhouse emissions from a thermal power generation plant.
According to the present invention, there is provided a process for reducing a greenhouse gas emission component of a combustion gas from a thermal power generation plant, said process comprising:
injecting the combustion gas via an injection line into a discharge line through which a pressurized seawater stream from an elevated reservoir flows under a hydrostatic head so as to effectively dissolve or absorb at least a portion of the greenhouse gas emission component in the pressurized seawater stream to form a loaded seawater stream;
discharging the loaded seawater stream to an ocean via a bypass line or other outlet connected to the discharge line, whereby the emission of said greenhouse gas to the atmosphere is reduced; and
pumping seawater from the ocean to the elevated reservoir via the discharge line.
Preferably, injection of the combustion gas is conducted at times of non-peak power demand.
Advantageously, the thermal power generation plant operates in sequence with further use of the pressurized seawater stream including:
i) pumping of the seawater from the ocean;
ii) injecting the greenhouse gas into the seawater stream flowing under the effect of gravity into the ocean;
iii) generating peak electricity.
The process preferably further includes generating power via a hydroelectric power plant, the hydroelectric plant being operatively coupled to the discharge line.
Advantageously, a pre-conditioning step of passing the combustion gas through a catalytic converter is provided so as to increase in said combustion gas greenhouse gas concentration prior to contacting the combustion gas with the pressurized seawater stream.
Preferably, the discharge or disposal of the loaded seawater stream to the ocean including locating an outlet of the bypass line to flow into a deep ocean sink. Advantageously, the bypass line includes other outlets at predetermined depths so that the greenhouse gas component of the loaded seawater stream assists in marine growth.
In general, the pressurized liquid stream is seawater. Preferably, the seawater is a cooling stream of the thermal power station. More preferably, pressurization of the seawater cooling stream is effected by an elevated reservoir of said seawater which produces a hydrostatic head within the seawater stream.
Preferably, the combustion gas is injected into the seawater under pressure. Advantageously, the combustion gas is injected via an injection line into a discharge line through which the seawater flows. In one embodiment, the injection line is tapped just downstream of combustion gas pumps which are connected to a flue stack or emission system of the thermal plant.
Preferably, the loaded liquid stream is discharged to the liquid body, such as the ocean, via a bypass line which is connected to the discharge line.
Preferably, injection of the combustion gas into the pressurized stream is in sequence with other uses of the pressurized stream. Advantageously, injection of the combustion gas is conducted at times of non-peak power demand.
Advantageously, the thermal power generation plant operates on the following cycle:
i) pumping of seawater from the ocean to the elevated reservoir via the discharge line;
ii) injecting the greenhouse gas into the seawater stream flowing under the effect of gravity from the elevated reservoir via the discharge line and the bypass line into the ocean; and
iii) generating peak electricity.
In one embodiment the periods for which steps i), ii) and iii) are performed daily are approximately 12, 10 and 2 hours, respectively. Accordingly, the process can be specifically designed to provide relatively high levels of power generation during peak periods and reduced power generation during off-peak periods. By varying the parameters of time, size of equipment such as pumps, and pressure, greenhouse gas emissions can be reduced from between 0 and 100%.
Advantageously, the process for reducing greenhouse gas emissions includes the step of pumping seawater from the ocean to the elevated reservoir via the discharge line. In this instance, one or more pumps are used to pump seawater to the reservoir. Typically seawater is pumped from the ocean via one or more seawater intake pipes.
Preferably, the process also involves generating power via a generator of a conventional hydroelectric power plant, the hydroelectric plant being operatively coupled to the discharge line. Power generation by the hydroelectric plant is connected to the electrical grid.
The process for reducing greenhouse gas emissions preferably includes a pre-conditioning step of passing the combustion gas through a catalytic converter so as to vary the composition of greenhouse gases prior to contacting the combustion gas with the pressurized liquid stream.
Preferably, the discharge or disposal of the loaded liquid stream to the ocean involves locating an outlet of the bypass line so the discharge will flow to a relatively deep ocean sink. Additionally, the bypass line may include other outlets being arranged at predetermined depths so that the greenhouse gas component of the loaded liquid-stream assists in marine growth.